FR3058927A1 - TREAD WITH RIBS INCLUDED - Google Patents

Abstract

Tread (1) for a truck tire, said tread comprising at least one circumferential rib (2) of width Lr, said circumferential rib (2) comprising a plurality of incisions (41, 51) delimiting a plurality small elements (6) of material with a density D at least equal to 15 small elements and at most equal to 80 small elements per decimetre squared, each small element (6) being delimited by incisions (41, 51) adapted to closing at least partially during the passage in the contact with a roadway, this tread (1) being such that the incisions (41, 51) delimiting the small elements (6) open into hidden channels (52), these channels concealed (52) being interconnected to provide a network for the continuity of a fluid flow.

Description

Holder (s): COMPAGNIE GENERALE DES ETABLISSEMENTS MICHELIN Limited partnership with shares, MICHELIN RECHERCHE ET TECHNIQUE S.A. Limited company.

Extension request (s)

Agent (s): MANUFACTURE FRANÇAISE DES PNEUMATIQUES MICHELIN.

(04 / TREAD BELT HAVING INCISED RIBS.

FR 3 058 927 - A1 (5f / Tread (1) for a truck tire, this tread comprising at least one circumferential rib (2) of width Lr, this circumferential rib (2) comprising a plurality of incisions (41, 51) delimiting a plurality of small elements (6) of material according to a density D at least equal to 15 small elements and at most equal to 80 small elements per square decimetre, each small element (6) being delimited by incisions (41, 51) capable of closing at least partially during the passage in contact with a roadway, this tread (1) being such that the incisions (41,51) delimiting the small elements (6) open into hidden channels (52), these hidden channels (52) being interconnected in order to produce a network allowing the continuity of a fluid flow.

-1 2016PAT00211 FR

TREAD COMPRISING INCISED RIBS

FIELD OF THE INVENTION (0001) The invention relates to treads for tires and more particularly to the tread patterns of these bands as well as to tires provided with such bands, the wear performance of which is improved while providing high performance in grip.

State of the art (0002) In a known manner, driving conditions in rainy weather require the fastest possible elimination of the water between the tread of each tire and the roadway in order to ensure contact with the tire. tread with the roadway. The water which is not repelled on the front of the tire partly flows in the grooves and the incisions formed in the tread of the tire whether these grooves and incisions are oriented in the circumferential direction or the transverse direction or still in an oblique direction.

(0003) Definitions (0004) The tread surface of a tread corresponds to the external surface of the tread intended to come into contact with a roadway when rolling a tire provided with this tread.

(0005) Cutting means any cavity produced in particular by molding in a tread, this cavity extending both in a main direction corresponding to its largest dimension on the rolling surface and in the direction of the thickness of the tread.

(0006) Here, a groove is understood to mean a cut opening on a rolling surface intended to be in contact with the road, this cut having an average width

-2 appropriate so that the walls of material which delimit it are never in contact with each other under normal conditions of use of the tire.

(0007) By incision is meant here a thin cut having a small average width and such that, under normal conditions of use of the tire, the walls of material delimiting the thin cut can come, at least partially, into contact with the one on the other when passing through the region of contact with the roadway.

(0008) By hidden channel or hidden groove is meant a cavity formed under the new rolling surface, this hidden cavity being able to be intended to form a new groove opening on the rolling surface after a predetermined partial wear of the strip. rolling. This cavity can also remain completely hidden regardless of the level of wear before the legal wear limit. A hidden channel is delimited by two side walls facing each other, these two side walls being connected together by a lower part forming a bottom connecting the two walls radially inwards and by an upper part in the extension of these walls radially outwards. In this upper part can open an incision connecting the hidden groove to the new rolling surface.

(0009) By thickness of material to be used, is meant the thickness of the tread which can be worn during driving before reaching the legal limit of use, this limit being able to be indicated by indicators of wear limit formed by example in the grooves.

(0010) A surface trough rate is calculated as the ratio between the trough surface opening on the rolling surface and the total surface including the material surface and the trough surface. You can define a surface trough rate for part of a tread or for the entire width of the tread. Likewise, it is possible to define a surface hollow rate in new condition and a surface hollow rate after partial wear.

(0011) A volume trough rate is calculated new as the ratio between the volume of all the troughs formed in a new tread and a total volume making the sum of the volume of all the troughs and the volume of material.

-3 (0012) In the present description, the terms "radial" or "radially" are used to indicate a direction which, when taken from the tire, is a direction perpendicular to the axis of rotation of the tire while , when taken on a tread alone, it corresponds to the thickness of said strip. Furthermore, the term circumferential is used to indicate a direction which corresponds to a direction tangent to any circle centered on the axis of rotation of the tire. This same direction corresponds to the longitudinal direction of the tread, the latter being formed in the manner of a flat strip before use for the manufacture of a tire.

(0013) Whatever the tire category (that is to say, whether it is a tire fitted to a passenger vehicle or a vehicle intended to carry heavy loads), the tread must have a drainage performance of the water present on the road which is always above a minimum performance called safety performance. Consequently and taking into account the progressive wear of the tread which progressively reduces the cross-sectional areas of the grooves and consequently the capacity of these grooves to evacuate a volume of liquid, it is usual to make grooves leading to the running surface in new condition and extending in the thickness of the strip to at least a level which corresponds to a legal limit requiring the removal of the strip.

(0014) The production of a plurality of grooves on a tread in this way has the drawback of reducing the quantity of strip material for a given strip width and consequently of significantly affecting the stiffnesses of the strip. bearing and wear performance. As a result, in order to cope with the stresses borne by the strip during rolling, the person skilled in the art must plan to compensate for these decreases in stiffness by any means at his disposal, in particular by adapting the internal structure of the tire which, of course , is not without impact on the cost price of the tire itself.

In the past, it has been proposed to distribute the volume of the cutouts differently between the grooves and the incisions by forming a very large number of incisions delimiting a very large number of small pieces of material, these incisions being capable of close completely when passing through the contact so that the small elements are in contact with one another in this contact region. The documents

- 4EP2339700B1 and EP2397345B1 show such achievements. Each small element comprises a contact face forming a part of the running surface of the tread, this contact face being intended to come into contact with the road during driving and lateral faces cutting the contact face to form edges. These lateral faces are at short distances from the lateral faces of the small neighboring elements so as to be in contact with them at least in part when passing through the contact. An incision closes completely as soon as the walls which delimit it come into contact with each other on at least 80% of their surface.

(0016) By small element is meant in this document an element of material delimited by incisions and whose contact face radially outside is intended to form a part of the tread surface of the tread coming in. contact with the roadway. In addition, the density D in small elements per square decimetre is between 15 and 80.

(0017) This density D is calculated over the width of a rib using the following formula:

(0018) D = N / [P x W x (1-Rib surface area rate)] (0019) In which:

(0020) P: is the circumferential length expressed in decimeters of a rectangular window containing in the circumferential direction five rows of small elements, (0021) W: is the width expressed in decimeters of this same window containing in the transverse direction all the small elements of the rib considered, (0022) N corresponds to the total number of small elements in the rectangular window of circumferential length P and transverse width W.

(“Rib surface trough rate” is calculated as indicated above in this document for the rectangular window considered of dimensions P, W on the considered rib of the new tread and is therefore equal to the ratio between the surface hollows on the rib considered and the total surface of the rib considered summing the contact surfaces of the small elements and those of the hollows.

- 5 (0024) However, it has been observed that tires for heavy goods vehicles fitted with such treads could develop faster wear due to effects of localized overpressure on the edges when the contact enters and leaves. In certain configurations, this wear, in addition to the fact that it can be faster, can also be irregular, that is to say that it does not regularly and uniformly affect the whole of the tread surface. These locally more pronounced wear develops in particular in the vicinity of the edges of the small elements.

Brief description of the invention (0025) The objective of the invention is to solve this problem of faster wear which can be generated by the presence of a plurality of small elements while limiting the mechanism of irregular wear which may occur. on the edges of small elements.

To this end, the invention relates to a tread for a heavy vehicle tire having a total thickness corresponding to the thickness of the material to be used in driving. This tread has a new tread surface intended to come into contact with a roadway when rolling a tire provided with this tread.

(0027) The tread according to the invention comprises at least one circumferential rib of average width Lr, this circumferential rib comprising a plurality of incisions delimiting a plurality of small elements of material, according to a density D which is at least equal to 15 small elements and at most equal to 80 small elements per square decimetre, this density D being calculated by the following formula: (0028) D = N / [P x W x (1-surface trough rate)], in which:

(0029) P is the circumferential length expressed in decimeters of a rectangular window containing in the circumferential direction five rows of small elements, (0030) W is the width expressed in decimeters of this same window containing in the transverse direction all the small elements of the rib considered, (0031) N corresponds to the total number of small elements in the rectangular window of circumferential length P and transverse width W.

- 6 (0032) Each small element is delimited by incisions capable of closing at least partially when passing in contact with a roadway so that the small elements are pressed against each other when passing through the contact.

(0033) Each small element comprises at least three lateral faces and a contact face radially on the outside, the lateral faces cutting the contact face along edges.

(0034) This tread is such that the incisions delimiting the small elements open in hidden channels, these hidden channels being connected together in order to create a network allowing the continuity of a fluid flow. In addition, these channels modulate the compression stiffness of the parts of material located between the edges of the small elements and said channels. This modulation improves the wear of the tread.

(0035) It was chosen to size the window by fixing the number of rows of small elements at five, but any other whole number could have been taken.

(0036) It is also advantageous that the surface hollow ratio of nine measured on each rib comprising a plurality of small elements is at most equal to 5% and even more preferably at most equal to 3%.

(0037) Preferably, the hidden channels have a maximum height H2 and a maximum width L2. The height H2 of the hidden channels is preferably between 15% and 40% of the total depth H of the incisions, this total depth H adding the height of the channels H2 and the depth H1 of the incisions.

(0038) In addition, the maximum width L2 is between 10% and 30% of the maximum circumferential length Lb of the small elements.

Advantageously, the channels are intended to form new grooves after a predetermined partial wear.

Advantageously, the hidden channels are arranged in the tread so as not to transform into new grooves before the tire is removed for wear of its tread; thus, the hidden channels do not appear on the surface

- 7 rolling during the use of the tire; these channels remain completely hidden regardless of the wear level of the tape.

Thanks to this invention, it is possible to locally modify the crushing stiffness of the tread and thus to modify, near the edges of the small elements, the contact pressures at the input and at the output of contact with the road. .

(0042) This local change in stiffness ensures better wear performance and it is thus possible to obtain a more regular tread wear profile whether or not new grooves appear compared to the same tread. devoid of hidden channels as defined.

Other features and advantages of the invention appear from the description given below with reference to the accompanying drawings which show, by way of non-limiting example, an embodiment of the object of the invention.

Brief Description of the Figures (0044) Figure 1 shows a partial view of a tread according to the invention comprising a central rib provided with a plurality of incisions in the circumferential direction and in the transverse direction;

(0045) Figure 2 shows an enlarged view of the running surface of the tread of Figure 1 on a window of circumferential dimension P and transverse dimension W;

(0046) Figure 3 shows a sectional view of Figure 2 along a section plane whose trace in Figure 2 is identified by line III-III;

(0047) Figure 4 shows an alternative arrangement of small elements on a rib of a tire according to the invention;

(0048) Figure 5 shows another variant of arrangement of small elements on a rib of a tire according to the invention.

- 8 Description of the figures (0049) To simplify the reading of the description of the examples of embodiment of the same reference signs are used to designate structural elements when they fulfill the same technical function although of different shapes.

(0050) Figure 1 shows a partial view of a tread 1 of a tire according to the invention of dimension 315/70 R 22.5, this tread 1 comprising a circumferential central rib 2 delimited by two circumferential grooves 3 This central rib 2 has a width Lr and is provided with a plurality of incisions 41 oriented in the circumferential direction and with a plurality of incisions 51 oriented in the transverse direction. All of these incisions 41, 51 formed by molding on the central rib 2 are capable of closing at least in part when passing through the contact during the rolling of the tire provided with this tread 1. In the example described, the incisions 41, 51 have average widths equal to 0.6 mm and can be closed, that is to say that more than 50% of their facing wall surfaces are in contact. The incisions 41 and 51 all extend respectively by channels 42, 52 communicating with each other and going around each small element 6. In the example presented, the channels 42 and 52 have the same section geometry. These channels communicate with the circumferential grooves 3.

(0051) These circumferential 41 and transverse 51 incisions delimit a plurality of small elements 6, the contact face 60 of which is square on the running surface 10 of the tread 1. Each edge 61 of the small elements 6 has the length Lb which is equal to 20 mm in the example described.

(0052) As can be seen in this figure 1, the surface hollow ratio new is very low for the central rib 2 and is in the present case equal to 1.5%; this surface trough rate is reduced moreover during the passage in contact since the incisions tend to close.

(0053) Figure 2 shows an enlarged view of the tread surface of the tread of Figure 1. We isolated on a rectangular window F of dimension P and transverse width W. The dimension P corresponds to the circumferential length of the

- 9 window framing five rows of small elements 6 in the circumferential direction on the rib 2.

In the present case, the density D in small elements 6 per square decimetre is equal to 25.38.

(0055) This density D is calculated with the following formula:

(0056) D = N / [P x W x (1-surface trough rate)] (0057) In which:

(0058) P: is the circumferential length expressed in decimeters of a window containing in the circumferential direction five rows of small elements, (P is

1 dm) (0059) W: is the width expressed in decimeters of this same window containing in the transverse direction all the small elements of the rib considered, (W is in this case equal to the width Lr of the central rib and is worth 0.8 dm), (0060) N corresponds to the total number of small elements in the rectangular window of circumferential length P and transverse width W. Here this number is equal to 20.

(0061) Figure 3 shows a sectional view of Figure 2 along a section plane whose trace in Figure 2 is identified by line III-III. In this FIG. 3, it can be seen that each transverse incision 51 (the direction XX ′ indicates the circumferential direction on the tire) has a total depth Ht (here equal to 10 mm) and is extended by a channel 52 of maximum width L2 (in the present case 2.2 mm) and maximum height H2 (here equal to 4.5 mm). The incision is 0.6 mm wide. The total depth of the incision 51 and of the channel 52 is denoted H. This total depth H is equal to the depth of the circumferential grooves 3 delimiting the central rib 2.

(0062) The height H2 (4.5 mm) of the channels 52 is preferably between

15% and 40% of the total depth H (14.5 mm).

(0063) Figure 4 shows an alternative arrangement of small elements 6 on a rib 2 of a tire according to the invention. In this particular case, each small element 6 has a contact face 60 of hexagonal shape which is more elongated in the circumferential direction (denoted XX ’) than in the transverse direction.

-10 (0064) This geometry of the contact face is particularly advantageous since it allows substantially identical mechanical operation in the circumferential direction and in the transverse direction. This geometry finds its application for tires intended to equip a driving axle or else a steering axle of a heavy vehicle.

(0065) It is possible to modify the dimensional aspect of the hexagonal elementary shape of the contact face, therefore of the section of small elements, to adapt the ratio of rigidities in the circumferential and transverse directions.

Furthermore, we see that each small element 6 located at the edge of a groove 3 has 10 a contact surface with the new ground which is at least greater than 80% of the average surface of the small elements 6 of the window. rectangular to which it belongs. By this arrangement it is possible to adjust the shape of the small elements at the edge of the groove while maintaining a minimum rigidity.

(0067) Figure 5 shows another variant of the arrangement of small elements 6 of 15 on a rib 2 of a tire according to the invention. In this particular case, each small element 6 has a contact face of triangular shape.

(0068) The triangular shape increases the flexibility of the tread.

In this variant, the width W of the rectangular window F is fixed so that this window passes through the axially outermost points of the smallest outermost elements (i.e. those bordering the grooves 3).

(0070) The invention is not limited to the two examples presented and various modifications can be made without departing from its scope as defined by the claims. In particular, it is possible in the same tire to provide that all the ribs are provided with small elements delimited by incisions as shown with the example described with FIGS. 1, 2 and 3.

- he -

Claims (8)

1 - Tread (1) for a truck tire, this tread 5 bearing (1) having a total thickness corresponding to the thickness of material to be used in rolling, this tread having a new rolling surface intended to come into contact with a roadway during the rolling of a tire provided with this strip, this tread comprising at least one circumferential rib ( 2) of width Lr, this circumferential rib (2) comprising a plurality of incisions (41, 10 51) delimiting a plurality of small elements (6) of material according to a density D at least equal to 15 small elements and at most equal to 80 small elements per square decimeter, this density D being calculated by the following formula: D = N / [P x W x (1-Rib surface area rate)], in which: P: is the circumferential length expressed in decimeters of a rectangular window 15 containing in the circumferential direction five rows of small elements, W: is the width expressed in decimeters of this same window containing in the transverse direction all the small elements of the rib considered, N corresponds to the total number of small elements in the rectangular window of circumferential length P and transverse width W, 20 the rate of surface area of the rib being, for each rib concerned in new condition, equal to the ratio between the surface of the hollows on the rib and the total surface of the rib summing the contact surfaces of the small elements and those of the hollows, each small element (6) being delimited by incisions (41, 51) capable of closing at least partially when passing through contact with a roadway, 25 this tread (1) being characterized in that the incisions (41, 51) delimiting the small elements (6) open into hidden channels (52), these hidden channels (52) being interconnected in order to achieve a network allowing the continuity of a fluid flow. - 122- Tread (1) according to claim 1 characterized in that the rate of surface hollow new measured on each rib (2) formed of a plurality of small elements (6) is at most equal to 5%. 3- Tread (1) according to claim 2 characterized in that the surface hollow ratio new measured on each rib (2) provided with a plurality of small elements (6) is at most equal to 3%. 4- Tread (1) according to any one of claims 1 to 3 characterized in that the maximum height H2 of the channels (52) is between 15% and 40% of the total depth H, this total depth H being equal to the depth H1 of the incisions (41, 51) increased by the maximum height H2 of the channels and in that the maximum width L2 of the channels is between 10% and 30% of the maximum circumferential length Lb of the small elements. 5- Tread (1) according to any one of claims 1 to 4 characterized in that the channels (52) are intended to form new grooves after predetermined partial wear. 6- Tread (1) according to any one of claims 1 to 4 characterized in that the channels (52) are arranged in the tread so as not to transform into new grooves before removal for wear. 7 - Tread (1) according to any one of claims 1 to 6 characterized in that each small element (6) in contact with a groove (3) has a contact surface with the ground at least nine at least greater to 80% of the average surface of the small elements (6) of the rectangular window to which it belongs. 8 - Tire for heavy goods vehicle comprising a tread (1) according to any one of claims 1 to 7. 1/2